Input devices including touch sensor devices (e.g., touchpad sensors, touch screen displays, etc.), as well as fingerprint sensor devices, are widely used in a variety of electronic systems.
Touch sensor devices typically include a sensing region, often demarked by a surface, in which the touch sensor device determines position information (e.g., the presence, location, and/or motion) of one or more input objects, typically for purposes allowing a user to provide user input to interact with the electronic system. Fingerprint sensor devices also typically include a sensing region in which the fingerprint sensor device determines fingerprint information (e.g., images of a full or partial fingerprint pattern, fingerprint features such as ridges or minutia, etc.), typically for purposes relating to user authentication or identification of a user.
Touch sensor devices and fingerprint sensor devices may thus be used to provide interfaces for the electronic system. For example, touch sensor devices and fingerprint sensor devices are often used as input devices for larger computing systems (such as opaque touchpads and fingerprint readers integrated in or peripheral to notebook or desktop computers). Touch sensor devices and fingerprint sensors are also often used in smaller computing systems (such as touch screens integrated in mobile devices such as smartphones and tablets).
Fingerprint sensor devices designed to capture fingerprint information typically differ from touch sensor devices that are designed to merely detect position information of a finger in a few ways. Most notably, capturing fingerprint information involves sampling much smaller structures than a typical touch sensor. While a touch sensor may be designed to sample an overall fingertip (e.g., on the order to approximately 5 mm in size or greater), a fingerprint sensor may be designed to sample individual surface variations on a fingertip surface (e.g., on the order of approximately 500 microns in size or less). As a result, the fingerprint sensor typically has a much higher spatial density of sensing elements than the touch sensor.
Some sensors used for touch sensing in a display area involve transparent electrodes (e.g., indium tin oxide (ITO)) to minimize the impact on visible graphics that are transmitted through the sensor device. Other sensors used for touch sensing involve opaque metals (e.g., copper) arranged in a fine but sparse grid of interconnected metal traces (sometimes known as “metal mesh”) to effectively create larger sensor electrodes suitable for touch sensing while maintaining sufficient overall transparency that allows the graphics to be displayed through these interconnected traces.
Unfortunately, these sensors do not provide electrical properties suitable for capturing fingerprint information, nor do these sensors provide a sensing array that is both sufficiently dense enough to capture fingerprint information while remaining suitably transparent for integration within a display active area.